An engineered viral protein rewires signaling pathways to activate STAT5 and sustain T cell functionality in tumors 4715

Abstract Description Cytotoxic CD8+ T cells can mediate the elimination of cancer cells but are typically inactivated within solid tumors. The suppressive environment within tumors deprives T cells of the cytokine-induced JAK-STAT signals needed for their survival and function. We therefore engineered a viral protein to directly activate endogenous STAT proteins in T cells. These STAT activators bind a non-JAK tyrosine kinase and recruit it to a targeted STAT to phosphorylate and activate it. A STAT5 activator (aSTAT5) was evaluated in primary CD8+ T cells and found to sustain T cell survival ex vivo in the absence of IL-2. We therefore evaluated tumor specific T cells transduced to express aSTAT5 using the suppressive B16-OVA model. We found that aSTAT5 decreased tumor growth due to a marked increase in the abundance of tumor specific T cells within the tumor and draining lymph node. aSTAT5 also reduced levels of PD-1 and maintained high Granzyme B levels indicating increased functionality. We therefore conducted single cell RNA sequencing on intratumoral T cells and determined that aSTAT5 sustained expression of survival factors, such as Bcl2, and reduced genes associated with an exhausted T cell state, such as Tox, Lag3, and Pdcd1 (PD-1). As a consequence, aSTAT5 was found to reduce the proportion of exhausted CD8+ T cells within tumors. Our findings highlight that the signaling machinery of T cells can be rewired to stave off dysfunction within solid tumors and promote anti-tumor immunity. Funding Sources V Foundation Scholar Award; Concern Foundation Conquer Cancer Now Award; NIH R35GM146813; NIH T32GM140223; NIH T32GM145470 Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)